1. Field of the Invention
The invention relates to a method for natural suppression of sprouting of stored potatoes.
2. Description of Related Art
Typically, tubers are harvested, allowed to suberize (i.e., allow the "skin" or periderm layer to form over wound areas) at warm temperatures for about 10 days, then gradually cooled down to the storage temperature of about 10.degree. C. For the first 1-2 months after harvest, the tubers remain dormant and exhibit little inclination to sprout. However, after this period the tubers must be chemically treated or refrigerated at very cold temperatures to prevent sprouting from occurring, such sprouting causes numerous deleterious effects to the tubers. These include a loss of fresh weight, the conversion of starch to sugars, and a decrease in the quality and appearance of tubers sold fresh. Sprouts and the surrounding tissue also contain elevated levels of toxic glycoalkaloids, which are not destroyed by cooking.
Although sprouting may be inhibited by cold storage at very low temperatures (slightly above freezing), this technique is not only expensive, but also inflicts other deleterious affects upon the tubers, rendering them unsuitable for processing. As potato tubers age, or when they are subjected to very cold temperatures or other stresses, they convert starch to reducing sugars. The development of reducing sugars in the raw product is very undesirable because the sugars combine via aldol condensations with amino acids during processing to form dark melanoidin pigments. Even small accumulations of reducing sugars in the raw product result in an unacceptably dark and unmarketable finished product.
Chlorpropham (CIPC; 1-methylethyl-3-chlorophenylcarbamate) is currently used to control tuber sprouting throughout the industry. Although CIPC has been used effectively, it has been on the market for over three decades and no replacements or improvements to the technology of sprout control have been made commercially available during this time. In the U.S. and around the world, there is increasing emphasis on replacing synthetic control agents (agricultural chemicals) with natural biological control mechanisms that are safe and more environmentally acceptable.
For many centuries, the Incas of South America and their descendants buried potato tubers in pits that were layered with soil and the leaves of Muna plants that belonged to the mint family Lamiaceae, and the genera Minthostachys and Satureja. This treatment prevented sprouting and excessive fresh weight loss, and repeled insect pests. These Muna plants contain copious amounts of essential oils that are substantially comprised of monoterpenes. Aliaga and Feldheim [Ernahrung, 9:254-256 (1985)] and Feldheim ["Practicability and Mode of Action of Quality Storage of Potatoes After Harvest," In Report of a Lecture Given to the German Institute for Quality Research (Plant Nutrition Products), March 1985, 6 pages] reported that the oil from the Muna plants was more effective than CIPC in inhibiting sprouting, fresh weight loss, and the incidence of rotted tuber parts over a period of 120 days. The authors also reported that the main components of the oil, including the monoterpenes .alpha.- and .beta.-pinene and limonene, and the oxygenated monoterpenes pulegone and menthone/isomenthone, are effective in this regard.
Currently, several research groups in the United States and Europe are investigating alternative synthetic chemical inhibitors to tuber sprouting [Rama and Narasimham, J. Food Sci. Technol., 24:40-42 (1987)].
Vaughn et al. (U.S. Pat. No. 5,139,562) and Vaughn and Spencer (U.S. Pat. No. 5,129,951) disclosed that the oxygenated monoterpenes cineole, fenchone and menthol, as well as several aromatic aldehydes and alcohols, including thymol, hydrocinnamaldehyde, cuminaldehyde, salicylaldehyde, cinnamaldehyde, and benzaldehyde, may be advantageously used to inhibit potato tuber sprouting, fresh weight loss, rotting, and fungal growth. Vaughn and Spencer also reported that the aromatic acid, benzoic acid, did not inhibit tuber sprouting.